1. Field of the Invention
The present invention relates to an electromagnetically driven valve control apparatus for an internal combustion engine and, more particularly, to an electromagnetically driven valve control apparatus and an electromagnetically driven valve control method that electrically open and close an intake valve or an exhaust valve of an internal combustion engine.
2. Description of the Related Art
An electromagnetically driven valve that functions as an intake or exhaust valve of an internal combustion engine is disclosed, for example, in Japanese Patent Application Laid-Open No. HEI 9-195736. The electromagnetically driven valve has a spring that urges the valve to a neutral position, an upper electromagnet that draws the valve to a fully open position, and a lower electromagnet that draws the valve to a completely closed position. Thus, the electromagnetically driven valve may be opened and closed by supplying appropriate currents alternately to the upper and lower electromagnets.
The electromagnetic force needed to open and close an electromagnetically driven valve of an internal combustion engine varies depending on the operating condition of the internal combustion engine, the temperature of the electromagnetically driven valve, etc. In order to ensure reliable operation of an electromagnetically driven valve while using a minimum amount of power, it is desirable that the exciting current supplied to the electromagnets be controlled to a minimum required amount. In the aforementioned conventional electromagnetically driven valve, the waveform of the exciting current supplied to the electromagnets is changed in accordance with the operating conditions of the internal combustion engine, and the like.
However, the effect of external disturbances on the valve may not be constant even when the operating condition of the internal combustion engine and other conditions remain unchanged. Therefore, it is difficult to precisely determine a minimum electromagnetic force needed to operate the valve solely on the basis of the operating conditions of the internal combustion engine and the like. Consequently, in a valve apparatus as described above, it is desirable to consider variations in external disturbances in setting a waveform of the exciting current, more specifically, it is desirable to consider the greatest external disturbance that impedes operation of the valve.